Fluid distribution systems associated with heating, ventilating and air-conditioning (HVAC) distribution systems are well known in the art, and are widely used in commercial applications, including apartment buildings and office buildings, for example. Such systems also see widespread use in laboratory-type settings, and in such an implementation, the HVAC system must not only control the temperature of the air in the building, but must also exhaust potentially noxious fumes, particularly if the building has a number of laboratory fume hoods in which experimental work is being carried out. Another implementation that has additional important considerations in addition to controlling the temperature of the air in the building involves clean room environments where manufacturing of electronic integrated circuits and the like is carried out.
In both of these latter implementations, the pressure of a room of interest may have to be controlled to be different from the space or rooms adjacent to the room of interest. In the case of the clean room environment, the room of interest must be maintained at a differential pressure higher than the surrounding space to insure that contaminates do not enter the room. In the case of the laboratory environment, the room of interest is kept at a differential pressure less than the surrounding area to contain any noxious fumes in the room.
To maintain a room of interest at a desired differential pressure relative to the surrounding area, the HVAC system must be capable of controlling the flow of air into the room, and the flow of air being exhausted from the room, and must take into consideration any other air flow into and out of the room. Given the temperature control requirements that must be maintained in the room, it becomes a more complicated control problem that is not easily solved.
While variable air volume (VAV) control equipment has been used for providing a control strategy for the implementations discussed above, and such control equipment has utilized a combination of feedforward and feedback control methodology, there continues to be a need for an effective control apparatus that provides improved performance, ease of implementation and cost effectiveness.